This invention relates generally to processing within a computing environment, and more particularly to program status word dependency handling in a computing environment.
Program status words (PSW) are an area of memory or a hardware register that contains information about a program state used by the operating system and the underlying hardware. The PSW typically includes thirty two or sixty four bits that are divided into one or more fields. At least one field of the PSW typically includes a pointer (address) to the next instruction to be executed.
The fields of the PSW can be referenced either explicitly (e.g., when instruction execution reads part of the PSW bits as in instructions IAC, IPK, STOSM), or implicitly (e.g., in instructions fetching, operand fetching, address generation calculations, address generation sources, etc.). The explicit reference can be performed at execution time, whereas the implicit reference can be performed at different stages of the pipeline (i.e., instruction fetch, instruction decode, execution time and completion time). Individual fields in the PSW can be referenced or updated independently and thus, require special handling.